Blood vessel exhibits a complicated microstructure depending on the anatomical portion, which enables the realization of its proper mechanical function. In particular, tunica media plays crucial roles in mediating the structural and functional properties of blood vessels. However, the microstructural analysis with quantitative methodology has not been established. In this study, the quantitative analysis of collagen fibers and elastin fibers in tunica media was achieved by combination of a selective staining technique using fluorescent dyes and birefringence measurement with polarized microscopy. The present method quantitatively unveiled the microstructural difference between thoracic aorta and caudal artery. Both types of vessels were comprised of collagen fibers and elastin fibers running along the circumferential direction of tunica media. Interestingly, the degree of preferential orientation of these fibers was markedly increased in thoracic aorta, suggesting that the anisotropic microstructure of vessel varies depending on the anatomical site.

Schematic illustration of the procedure of quantitative analysis of anisotropic microstructures in tunica media of blood vessel. The preferential orientation of collagen fibers was quantified by polarized microscopy with birefringence system. The preferential orientation of elastin fibers was quantitatively analyzed with fluorescence microscopy followed by image and numerical processing.